The absorption, distribution, metabolism and excretion of 14C-labeled allyl isothiocyanate (AITC) was studied in male and female rats and mice. AITC was cleared from all rat and mouse tissues so that within 24 hours after administration less than 5% of the total dose was retained in the tissues. Clearance of AITC-derived radioactivity by each species was primarily in urine (70-80%) and as CO2 in exhaled air (10-15%) with lesser amounts in feces (2-5%). Over 98% of AITC was metabolized by rats and mice to 5 or 6 metabolites respectively. These results demonstrated significant species related differences in AITC metabolism and sex related differences in urine volume excreted. These variations result in exposure of male rat urinary bladders to significantly higher concentrations of an AITC metabolite for longer periods of time and may account for similar variations in sensitivity to bladder toxicity by AITC.